The bimodal score distribution of the test of English of the Basic Competence Test for Junior High School Students (BCTEST) has received great research interests since 2001. In this article, instead of discussing the social and educational issues, we applied psychometric and statistical methods to reconstruct the score distribution and explored the reasons and characters of the bimodality of the score distribution of the English test. It was found that assuming a normal ability distribution test items calibrated using different Item Response Theory models did not yield a bimodal score distribution. Second, it was demonstrated that the left-end mode might be caused by examinees' guesswork. Finally, the bimodal score distribution may be caused by the large ability variance and the threshold of test difficulty made by the English form item.